Portable drug delivery devices are used for the administration of a medicament or drug, especially a medicinal fluid that is suitable for self-administration by a patient. A drug delivery device may comprise a syringe, an injection device, an injector or a pen-type injection device. In particular, a drug delivery device in the shape of a pen is useful, since it can be handled easily and kept available everywhere.
There exist different types of drug delivery devices. One type of a drug delivery device comprises a disposable device which may be disposed after having dispensed the medicament or after the medicament has been expired. Another type of a drug delivery device comprises a refillable drug delivery device which may be reusable many times. This kind of drug delivery device may comprise a drive assembly and a cartridge holder which is connectable to the drive assembly and which contains a cartridge, ampoule or vial containing a medicament or drug. Often, a needle assembly may be connected to a distal end of the cartridge holder for subcutaneous injection of the medicament. A dose of a drug or medicament is delivered by means of a drive mechanism of the drive assembly driving a piston rod or lead screw in a distal direction, the piston rod interacting with a piston within the cartridge for expelling the medicament out of the device. The drug delivery device may provide a dose-setting mechanism which allows setting the dose of the medicament that is to be dispensed.
In common devices, as disclosed in U.S. 2009/0275914 A1 for example, the piston rod is guided in the drive assembly by a guide nut, also called body nut or lead screw nut, which is coupled to the piston rod for moving the piston rod in distal direction during drug delivery. For this purpose, the guide nut is rotationally fixed with respect to the housing of the drive assembly in order to urge the piston rod into a predetermined, mostly helical movement.
In reusable drug delivery devices the situation may arise that the drug delivery device has to be reset. This means, the piston rod has to be moved in a proximal direction opposite to the distal direction back into the drive assembly such that a new cartridge contained within the cartridge holder may be assembled to the drive assembly in order to start a new cycle of drug delivery. During the reset operation of the piston rod, the guide nut may preferably be rotatable with respect to the housing in order to enable a quick and easy shifting of the piston rod back into the drive assembly. Thus, the guide nut has to fulfill double functionalities, wherein during drug delivery the guide nut has to be rotationally fixed and during a reset operation the guide nut has to be rotatable with respect to the housing. This is also disclosed in U.S. 2009/0275914 A1.
According to U.S. 2009/0275914 A1 the drug delivery device provide a locking means for releasable engagement with the guide nut in order to prevent rotational movement of the guide nut with respect to the housing during drug delivery and to allow rotation of the guide nut with respect to the housing during resetting of the device. The locking means may directly be operated by the cartridge holder when the cartridge holder is assembled to the drive assembly.